Diabetes Mellitus is a heterogeneous mix of genetic abnormalities in the insulin-producing machinery ranging from the body's inability to produce enough insulin to the body's inability to recognize and/or use insulin. Type I diabetes is an autoimmune disease which systematically destroys insulin-producing β cells in the pancreas. Type II diabetes is caused by various genetic abnormalities in the pancreas and onset is directly correlated to obesity. The current standard treatment for diabetes is to maintain insulin levels by monitoring blood glucose and diet, to provide exogenous doses of insulin when necessary and to treat the consequences of diabetes such as loss of circulation to the extremities, glaucoma, and sepsis, as the disease progresses [Couper et al., Medical Journal of Australia, 179(8):441-447, 2003]. More radical treatments include full organ transplants, islet cell transplants or β cell transplants. Pancreatic transplantation candidates are put on a long waiting list for a suitable organ. Even when patients are lucky enough to be chosen for an allogeneic pancreatic organ transplant, they must take immunosuppressants in order to battle graft vs. host disease. A recent attempt to use islet cell transplant therapy provided short-lived relief in most patients but the transplanted β cells subsequently died or ceased to produce insulin in a majority of the initial successful transplants [Shapiro et al., New England Journal of Medicine, 355(13):1318-1330, 2006]. Clearly another approach is necessary to alleviate the problems caused by diabetes and address the root cause of the disease.
Recent developments in genome technologies, tissue engineering and synthetic biology offer possibilities to establish highly accurate and robust approaches for predictable and controllable cell fate regulation both temporally and spatially. Stem cell research promises to revolutionize the way many inherited and acquired diseases are treated and will also provide unprecedented insights into fetal development and the etiology of numerous disorders [Hochedlinger et al., N Engl J Med, 349(3):275-286, July 2003; Weissman, Science, 287(5457):1442-1446, February 2000; Lagasse et al., Immunity, 14(4):425-436, April 2001; Reya et al., Nature, 414(6859):105-111, November 2001]. Mouse embryonic stem (mES) cells are an attractive platform for this research because they are amenable to extensive genetic manipulation. When introduced into the appropriate in vitro or in vivo contexts, mES cells contribute to all tissue types of adult mice, including the germ line [Nagy et al., Development, 110(3):815-821, November 1990].
Consequently, there has been much excitement about the potential of these cells as an unlimited source of differentiated cell populations for transplantation or other therapies. Although potentially exciting and ground-breaking, ES cell-based therapies depend on the ability to reliably and controllably produce the necessary mature cell populations. In addition, directed differentiation must be absolute, given the tumorigenic potential of ES cells. With few exceptions, such directed production of desired cell populations has not been possible yet.
Current approaches towards tissue engineering and transplantation rely on carefully creating environments that induce cells to differentiate into desired tissues or organs. While these approaches have proven partially effective for certain applications, they are inherently limited since they rely on innate cellular response to existing host conditions or exogenous cues. Often, naturally occurring host conditions are insufficient to trigger the correct differentiation pathways. In those instances, researchers have attempted to provide appropriate environmental cues using scaffolds and exogenous signals. However, it is often difficult, if not impossible, to create and maintain the precise conditions that are required for tissue regeneration using such means.
What is needed in the art are systems and methods that can be used to cause stem cells to reliably differentiate into a desired cell type based on expression of genes introduced into the stem cells.